1. Field of the Invention
The present invention relates to an engine control equipment of the electronic control type and an air meter for the engine control equipment.
2. Description of the Prior Art
In an electronic engine control equipment for automobiles, the rate of fuel supplied to the engine (or the duration of a fuel injection pulse) is calculated by an engine control unit (microcomputer) having a function of inputting a signal indicating the rate of air flowing through an intake passage measured by the air meter, a signal representing the rate of revolutions of the engine, a coolant temperature signal, etc. and performing a digital operation on these signals. There have been various types of air meters for this type of engine control system. One of the most widely-used air meters uses a principle of a thermal air flow meter such as exothermic resistance elements whose resistance is dependent upon temperature as they are very small and can directly measure the mass and flow rate of air.
A conventional engine control equipment stores the standard air flow rate versus output characteristics table in advance in the engine control unit which works as the core of the engine control equipment and calculates the rate of intake air from a signal output from the air meter with reference to said table.
To calculate the rate of intake air using said table, a means is required which matches the actual air flow rate versus output characteristics of the air meter with a preset standard air flow rate versus output characteristics table (hereinafter mentioned as standard characteristics table) since each air meter product has specific output versus flow rate characteristics. It is well known that a typical one of such means consists of flowing air of a preset rate through two known different points and adjusting the amplification factor and the differential voltage of the differential amplifier provided on the output side of the air meter so that the outputs at these two points of the air meter may have the expected values (two points in the standard characteristics).
However, as the air flow versus output relation is not linear, it is technically hard to adjust said relation correctly. When you adjust the amplification factor and the differential voltage at one point to match two output signals with the expected values, the values on the other point may go off the expected values. To make this deviation smaller, you must repeat the above steps. Therefore, this adjustment is very time-consuming. Accordingly, presentation of a drastic adjusting method is expected.
When considered with the above description, a new art has been presented which calculates the rate of intake air from the corresponding sensor output in actual operation using the air flow rate versus output characteristics of the air flow sensor which is measured and stored in advance in a storage element built in the engine control unit. For example, such an art is described in Japanese Patent Application Laid-Open No. 64-73150.
Although the above latter art has a merit of omitting a step of matching the output characteristics of the air meter with the preset standard characteristics, said art becomes not applicable when the air meter is replaced by a new one.